package org.apache.lucene.store;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.util.HashSet;

/**
 * Implements {@link LockFactory} for a single in-process instance, meaning all
 * locking will take place through this one instance. Only use this
 * {@link LockFactory} when you are certain all IndexReaders and IndexWriters
 * for a given index are running against a single shared in-process Directory
 * instance. This is currently the default locking for RAMDirectory.
 * 
 * @see LockFactory
 */

public class SingleInstanceLockFactory extends LockFactory {

	private HashSet locks = new HashSet();

	public Lock makeLock(String lockName) {
		// We do not use the LockPrefix at all, because the private
		// HashSet instance effectively scopes the locking to this
		// single Directory instance.
		return new SingleInstanceLock(locks, lockName);
	}

	public void clearLock(String lockName) throws IOException {
		synchronized (locks) {
			if (locks.contains(lockName)) {
				locks.remove(lockName);
			}
		}
	}
};

class SingleInstanceLock extends Lock {

	String lockName;
	private HashSet locks;

	public SingleInstanceLock(HashSet locks, String lockName) {
		this.locks = locks;
		this.lockName = lockName;
	}

	public boolean obtain() throws IOException {
		synchronized (locks) {
			return locks.add(lockName);
		}
	}

	public void release() {
		synchronized (locks) {
			locks.remove(lockName);
		}
	}

	public boolean isLocked() {
		synchronized (locks) {
			return locks.contains(lockName);
		}
	}

	public String toString() {
		return "SingleInstanceLock: " + lockName;
	}
}
